This should find the number of tickets created in each Mon-Sun week, then take the average across weeks. You can combine this with Hour Ticket Created under HOW to get the average per week within each hour.

When filtering a report like this, I strongly recommend using the same units in the filter and metric. If you filter for the past 90 days, you'll end up with partial weeks on the boundaries. That will skew your results, since those partial weeks would have much lower results but be treated the same in the calculation. Try filtering for 13 weeks ago to 1 week ago to cover a similar period of time.

Also note - I used the week attribute that includes /Year. That locks it to specific dates in specific years. If I look for tickets "last week," Week (Mon-Sun)/Year (Ticket Created) would show me Dec 17, 2018, through Dec 23, 2018, while Week (Mon-Sun) (Ticket Created) would show me the 51st week across all years combined.